Tubes obtained from a propylene polymer composition

ABSTRACT

Tubes obtained from a propylene polymer based composition Tubes formed from a propylene polymer based composition having a module of elasticity at flexion of 1,400 to 2,000 MPa and a melt flow index of 0.1 to 1 g/10 minutes, including:  
     from 80 to 97 parts in weight of a propylene homopolymer (A) having an isotacticity index of at least 0.96, and  
     from 20 to 3 parts in weight of a statistical copolymer of propylene (B) containing from 45% to 70% ethylene mass and/or an alpha olefin containing from 4 to 8 atoms of carbon,  
     the ratio of the intrinsic viscosity of polymer (B) to polymer (A) being at least 1:55.

[0001] The present invention concerns tubes obtained from a propylenepolymer based composition. More specifically, it concerns tubes designedto transport low pressure fluids, such as domestic discharge or drainagetubes, obtained from a composition including a propylene homopolymer anda statistical copolymer of propylene.

[0002] We know how to use polypropylene to produce tubes designed totransport waste water. This is how document WO 99/35430 describes theuse of a composition containing 80 to 98 parts in weight of a propylenehomopolymer having an isotacticity index of at least 95%, from 2 to 20parts in weight of a propylene copolymer containing from 50 to 70 partsin weight of propylene and 50 to 30 parts in weight of ethylene, for themanufacture of tubes to be used for waste disposal. According to thisdocument, the ratio of the intrinsic viscosity of the copolymer to thatof the homopolymer must be between 0.9 and 1.5, and the composition musthave a melt flow index between 0.15 and 0.8 g/10 minutes, typically lessthan or equal to 0.2 g/10 minutes.

[0003] However, the compositions thus obtained do not have an optimalresistance to impact. In addition, obtaining melt flow indexes as low as0.2 g/10 minutes leads to excess production costs which make thesecompositions economically less profitable.

[0004] The purpose of the present invention is to produce tubes obtainedfrom a propylene polymer based composition which does not have thesedisadvantages.

[0005] In order to do this, the present invention involves tubesobtained from a propylene polymer based composition having a module ofelasticity at flexion of 1,400 to 2,000 MPa and a melt flow index of 0.1to 1 g/10 minutes, including:

[0006] from 80 to 97 parts in weight of a propylene homopolymer (A)having an isotacticity index of at least 0.96, and

[0007] from 20 to 3 parts in weight of a statistical copolymer ofpropylene (B) having from 45% to 70% ethylene mass and/or an alphaolefin containing from 4 to 8 atoms of carbon,

[0008] the ratio of the intrinsic viscosity of polymer (B) to polymer(A) being at least 1:55.

[0009] It goes without saying, in terms of the present invention, thatthe respective quantities of polymers (A) and (B) used are such thattheir sum is equal to 100 parts in weight.

[0010] The flexion module of the material (Flex Mod) is measured at 23°C. on an injected test piece of a thickness of 4 mm according to ISOstandard 178 and expressed in megapascals (MPa). The melt flow index,hereafter referred to simply as MFI, is measured under a load of 2.16 kgat 230° C. according to ASTM standard 1238 (1986) and expressed in g/10minutes.

[0011] The composition that can be used to manufacture tubes accordingto the present invention has the advantage of a Flex Mod of at least1,500 MPa. Flex Mods of more than 1,900 MPa give the tubes obtained withthese compositions optimal resistance to impact. It is also preferredthat the MFI of compositions that can be used according to the inventionbe at least 0.3 g/10 minutes. MFI's of more than 0.6 are especiallypreferred.

[0012] Compositions whose MFI is 0.3 to 0.6 g/10 minutes have theadvantage of having good properties at a lower cost and of being able tobe welded to a wider range of tubes.

[0013] The quantity of homopolymer (A) contained in the composition thatcan be used to manufacture tubes according to the invention has theadvantage of being at least 85 parts of the weight. Amounts ofhomopolymer (A) of at most 95 parts in weight give especially goodresults.

[0014] The propylene homopolymer (A) used in the composition that can beused to manufacture tubes according to the invention has an isotacticityindex (measured by the molar fraction of the isotactile triads accordingto the method described in relation to the examples) of at least 0.96,more specifically, at least 0.97. In general, the isotacticity index ofthe homopolymer (A) does not exceed 0.99.

[0015] The quantity of statistical copolymer (B) is most often no morethan 15 parts in weight, and quantities of at least 5 parts in weightare especially advantageous. In a preferred way [of manufacturing theinvention], the statistical copolymer (B) contains only polymer unitiesderived from ethylene.

[0016] Statistical copolymers containing from 35% to 60% in weight ofethylene are particularly well suited.

[0017] The content of comonomers mentioned in the present description isdetermined by Fourier transform infrared spectrometry on the polymertransformed into a pressed film of 200 μm. Absorption bands with 732 and720 cm⁻¹ are the ones used to determine the ethylene content. Theabsorption band with 767 cm⁻¹ is used to determine the 1-butene content.

[0018] The intrinsic viscosity of the polymers is measured in tetralineat 140° C. as described hereafter in relation to the examples.

[0019] One of the essential characteristics of compositions that can beused to manufacture tubes according to the invention is the use ofpolymers (B) and (A) as defined above and for which the ratio ofintrinsic viscosity is at least 1:55. By using such polymers, tubes canbe prepared which have the required properties of rigidity and goodresistance to impact at the same time. The maximal value of the ratio ofthe viscosity of polymers (B) and (A) is not critical. However, thisratio is preferably less than or equal to 3, more specifically, lessthan or equal to 2.5. Values between 1.6 and 2.3 give especiallyadvantageous results.

[0020] Within the scope of the present invention, compositions are mostoften used which have an elasticity module in flexion from 1,500 to1,900 MPa, a melt flow index of 0.3 to 0.6 g/10 minutes, including:

[0021] from 85 to 95 parts in weight of a propylene homopolymer (A)having an isotacticity index of at least 0.96, and

[0022] from 15 to 5 parts in weight of a statistical copolymer ofpropylene (B) having from 35% to 55% in weight of ethylene,

[0023] the ratio of the intrinsic viscosity of polymer (B) to polymer(A) being 1.6 to 2.

[0024] In spite of their relatively high melt flow index, suchcompositions have a rigidity/impact resistance ratio which is especiallywell adapted to the manufacture of tubes according to the invention.

[0025] The homopolymer (A) and the copolymer (B) that make up thecomposition that can be used for manufacturing tubes according to theinvention can be obtained by means of any known sufficiently productiveand stereospecific catalytic system, making it possible to polymerizepropylene in an isotactile form and to incorporate the required amountsof ethylene and/or alpha olefins. The intrinsic viscosity of thesepolymers can be adjusted by the addition of one or more molecular massadjusting agents, such as hydrogen, preferably. The viscosity of thesepolymers is generally adjusted so as to satisfy the ratio mentionedabove, as well as the final fluidity index of the compound.

[0026] Compositions that can be used to manufacture tubes according tothe present invention and that give the best results are obtained byusing polymers (A) and (B), obtained with the use of a catalytic systemincluding one solid containing, by way of essential components,titanium, magnesium, chlorine and an electron donor (internal electrondonor), an organoaluminum compound such as trialkylaluminum and, morespecifically, one of the alkylalkoxysilanes, preferably such as thediethyl- and dimethoxysilanes including two alkyl or cycloalkyl radicalscontaining, in alpha position, a secondary or tertiary carbon atom.Compounds of this type which give good results arediisobutyldimethoxysilane and dicyclopentyldimethoxysilane.

[0027] Such catalytic systems are well known to professionals in thefield. The components of the catalytic systems preferred according tothe invention are generally set up so that the molar ratio between thealuminum of the organoaluminum compound and the titanium of thecatalytic solid is 3 to 300, more specifically, 10 to 200. In addition,the preferred catalytic systems are such that the molar ratio betweenthe aluminum of the organoaluminum compound and the silicon of thesilicon compound is 0.5 to 10, more specifically, 1 to 4.

[0028] The composition that can be used to manufacture tubes accordingto the invention have the advantage of containing at least 50% in weightof polymers (A) and (B), more specifically, at least 90% in weight inrelation to the total weight of the composition.

[0029] In addition to polymers (A) and (B), the composition that can beused to manufacture tubes according to the invention may contain variousadditives which are generally not more than 50% in weight, preferably10% in weight in relation to the total weight of the composition. Thecomposition that can be used according to the invention can, inparticular, contain other polymers, load materials, stabilizers,pigments, antacids or nucleation agents. Preferably, the mixtureaccording to the invention contains in the way of polymers only polymers(A) and (B) defined above.

[0030] Compositions containing from 0.05% to 1% in weight of anucleating agent give particularly good results. Among these nucleatingagents, sodium benzoate is preferred for reasons of rigidity/cost ratio.It is also observed that the compositions that can be used tomanufacture tubes according to the invention that contain 0.01% to 0.5%in weight of an antacid and from 0.1% to 1% in weight of an antioxidantare better. By way of an antioxidant, encumbered phenols, phosphites,organosulfur compounds and/or their mixtures are used most often.

[0031] Preferably, the compositions that can be used to manufacturetubes according to the invention do not contain significant amounts ofload material. In fact, it is seen that amounts less than or equal to 5%in weight suffice to obtain good properties along with satisfactoryeconomic conditions.

[0032] The composition that can be used according to the presentinvention can be obtained by any appropriate technique. One can, forexample, mix the homopolymer (A) and the copolymer (B) and possibleadditives together according to any known process whatsoever, such as amelt mixture of the two preformed polymers. However, processes duringwhich the polymers (A) and (B) are prepared in two successive stages ofpolymerization are preferred. The polymer thus obtained is generallycalled a sequenced propylene copolymer. Generally, the homopolymer (A)is first prepared, and then the copolymer (B) is prepared in thepresence of the homopolymer (A) from the first stage. These stages caneach be done independently of each other, in a suspension, in an inerthydrocarbon diluent, in propylene maintained in the liquid state or evenin the gaseous state, on an agitated bed or, preferably, on a fluid bed.

[0033] Polymers (A) and (B) are mixed, preferably, in two successivestages of polymerization, in a gaseous phase in a reactor with a fluidbed using the preferred catalytic system described previously.

[0034] In this particular case, possible additives are also most ofteninserted during a later stage of melt mixing of the additives andpolymers.

[0035] The composition that can be used to manufacture tubes accordingto the invention can be made according to any known process for themanufacture of formed objects. It is especially suitable formanufacturing tubes and, more specifically, for the manufacture byextrusion of tubes designed for the transport of low pressure fluid. Inaddition to improved rigidity, the tubes manufactured using thecomposition have good impact resistance.

[0036] The following examples are intended to illustrate the invention.The techniques for measuring the sizes mentioned in the examples, theunits expressing these sizes and the meaning of the symbols used inthese examples are explained below.

[0037] The viscosity of the polymers is measured in tetraline at 140° C.using an Ostwald viscometer on solutions with 1.5 g/l of polymer.

[0038] The fractions of polymer soluble in xylene (XS) are determined byputting 3 g of polymer in a solution in 200 ml of metaxylene at boilingtemperature, cooling the solution to 25° C. by immersion in a water bathand filtering the soluble fraction at 25° C. on filter papercorresponding to a normalized G2. MF1: fluidity index of the compositionmeasured under a load of 2.16 kg at 230° C. according to ASTM standard1238 (1986) Total C2: total content in ethylene expressed in % in weightin relation to the weight of polymer (A) and polymer (B), measured on asample of the sequenced polymer transformed into a pressed film of 200μm by infrared spectrometry from bands of 732 and 720 cm⁻¹ [A]: amountof polymer (A) present in the composition in relation to the totalweight of polymer (A) and polymer (B), expressed in % and estimated fromthe equation: [A] = 100 − [B] [B]: amount of polymer (A) present in thecomposition in relation to the total weight of polymer (A) and polymer(B), expressed in % and estimated from soluble fractions of polymers [A]and [B] and their mixture C2 (B): ethylene content of copolymer (B)expressed in % in weight in relation to the total weight of polymer (B)and determined by applying the following equation: C2(B) = total C2 ×100/(B) II: Isotacticity index of polymer (A), characterized by themolar fraction of isotactic triads (sequenced chain of three propylenemonomer units in a meso configuration). This value is determined on asample of polymer (A) by nuclear magnetic resonance in 13C as describedin Macromolecules, volume 6, no. 6, p. 925-926 (1973) and in references(3) to (9) of that publication. β/α: ratio of the intrinsic viscosity ofpolymer (B) to polymer (A) determined from the equation: β = (η −[A])/[B] in which η represents the viscosity of the mixture α α 100 100of polymers (A) and (B) Flex. Mod.: Flex-module of the compositionmeasured as previously indicated in the description. Charpy: Resistanceto impact measured according to ISO standard 179/1 cA

[0039] Flex. Mod.: Flex-module of the composition measured as previouslyindicated in the description.

[0040] Charpy: Resistance to impact measured according to ISO standard179/1cA

EXAMPLES 1 (ACCORDING TO THE INVENTION) AND 2R (GIVEN BY WAY OFCOMPARISON)

[0041] Sequenced copolymers containing a homopolymer of propylene(polymer (A)) and a statistical copolymer (polymer (B)) were prepared bypolymerization in a gaseous phase in a fluid bed in two successivestages, in the presence of a catalyst with a magnesium chloride basecontaining 2.6% in weight of titanium and 11% in weight ofdiisobutyl-phthalate (internal electron donor), triethylaluminum anddicyclopentyl-dimethoxysilane in respective quantities, such as themolar ratio Al/Ti=75 and Al/Si=2. A sample of polymer (A) was taken foranalysis at the end of the first stage.

[0042] The conditions of polymerization, as well as the properties ofthe sequenced polymers, are given again in Table 1 hereafter.

[0043] One hundred parts in weight of these sequenced polymers are thenprocessed in a ZSK 30 extruder (sold by the Werner & Pfeider company) ata temperature of 230° C. together with:

[0044] 0.2 parts in weight of pentaerythrityl tetrakis(3,5-ditert-butyl-4-hydroxyphenyl propionate) sold under the nameIRGANOX® 1010 by the firm CIBA GEIGY,

[0045] 0.1 parts in weight of tris (2,4-ditert-butylphenyl) phosphitesold under the name IRGAFOS®;

[0046] 0.2 parts in weight of DSTDP (distearylthiodipropionate) soldunder the name IIOSTANOX®,

[0047] 0.05 parts in weight of hydrotalcite DHT-A4, and

[0048] 0.2 parts in weight of sodium benzoate.

[0049] The MFI and the Flex Mod, as well as other properties ofcompositions thus obtained, are also reviewed in the following Table 1.

[0050] It is thus seen that the composition that can be used accordingto the invention has a slightly better rigidity/impact resistance ratioin spite of a high MFI.

[0051] These compositions were then processed for the manufacture oftubes by extrusion of granules by a monoscrew type extruder (Battenfeldtype) at 210° C. TABLE 1 Characteristics Example 1 Example 2RPolymerization—polymer (A) Pressure (bars) 32 32 Temperature (° C.) 6565 Staying time (hours) 2 2 Molar ratio of H2/propylene in the gas0.0017 0.001 (mol/mol) Polymerization—polymer (B) Pressure (bars) 20 20Temperature (° C.) 72 72 Staying time (hours) 1.53 1.59 Staying time(hours) 0.0214 0.0189 Molar ratio of H2/propylene in the gas 0.79 0.82(mol/mol) Total C2 (% in weight) 4.0 4.6 [A] (%) 91.7 91.1 II 0.98 0.98[B] (%) 8.3 8.9 C2 (B) (% in weight) 48.2 51.7 β/α 1.8 1.3 MFI (g/10minutes) 0.51 0.30 Charpy at 23° C. (kJ/m2) 80.4 77.6 Charpy at 20° C.(kJ/m2) 4.1 4.0 Flex. Mod. (MPa) 1,741 1,679 XS (A) (%) 1.6 1.6 XSmaterial (%) 8.7 9.2 XS (B) (%) 85 85

1- Tubes formed from a propylene polymer based composition having amodule of elasticity at flexion of 1,400 to 2,000 MPa and a melt flowindex of 0.1 to 1 g/10 minutes, including: from 80 to 97 parts in weightof a propylene homopolymer (A) having an isotacticity index of at least0.96, and from 20 to 3 parts in weight of a statistical copolymer ofpropylene (B) containing from 45% to 70% ethylene mass and/or an alphaolefin containing from 4 to 8 atoms of carbon, the ratio of theintrinsic viscosity of polymer (B) to polymer (A) being at least 1:55.2- Tubes formed from a composition according to claim 1, having a moduleof elasticity at flexion of 1,500 to 1,900 MPa, a melt flow index of 0.3to 0.6 g/10 minutes, and including: from 85 to 95 parts in weight of apropylene homopolymer (A) having an isotacticity index of at least 0.96,and from 15 to 5 parts in weight of a statistical copolymer of propylene(B) having from 35% to 55% in weight of ethylene, the ratio of theintrinsic viscosity of polymer (B) to polymer (A) being at least 1.6 to2. 3- Tubes according to claim 1 or 2 designed to transport low pressurefluids.